1. Field of the Invention
The present invention relates to a vertical type stage apparatus used in an exposure apparatus or the like to vertically hold a substrate such as a wafer to be exposed.
2. Related Background Art
In the manufacture of semiconductor devices, further micropatterning of transfer patterns has recently been demanded with an increase in the capacity of a semiconductor memory. For this reason, an X-ray exposure apparatus using X-rays such as synchrotron radiation as exposure light has been developed. In such an X-ray exposure apparatus, a wafer to be exposed is generally held in a vertical position. A vertical type substrate stage apparatus like the one shown in FIG. 10 is used.
A vertical type substrate stage apparatus E.sub.0 in FIG. 10 is constituted by an X-stage 102, a Y-stage 103, a wafer chuck 104, an X-driving unit (not shown), a pair of linear motors 105, and a constant tension spring 106. The X-stage 102 can reciprocate along an X-guide 102a, which is integrally formed with a base 101, in one direction (to be referred to as the X direction hereinafter) within a horizontal plane. The Y-stage 103 can reciprocate, in a vertical direction (to be referred to as the Y direction hereinafter), along a Y-guide 103a integrally formed with the X-stage 102. The wafer chuck 104 is arranged on the Y-stage 103. The X-driving unit serves to move the X-stage 102 in the X direction. The linear motors 105 drive the Y-stage 103 in the Y direction. The constant tension spring 106 serves to cancel out the gravitation of the Y-stage 103. Each linear motor 105 is constituted by a 10 linear motor stator 105a integrally formed with the X-stage 102, and a linear motor rotor 105b integrally formed with the Y-stage 103. The lower end of the constant tension spring 106 is integrally coupled to the Y-stage 103, while the upper end of the constant tension spring 106 is wound around a rotating shaft 106a rotatably supported on a bearing 103b integrally formed with the Y-guide 103a.
The wafer chuck 104 has a vertical suction surface 104a. The suction surface 104a chucks a wafer (not shown) by vacuum suction. The position of the wafer chuck 104 in the Y direction is monitored by a Y-interferometer 108a for receiving light reflected by a Y-mirror 107a mounted on one end of the Y-stage 103 in the Y direction. An output from the Y-interferometer 108a is negatively fed back to a Y-servo arithmetic unit 108b. The Y-servo arithmetic unit 108b drives each linear motor 105 to move the Y-stage 103 in the Y direction on the basis of the difference between a command signal transmitted through a command line 108c and the output from the Y-interferometer 108a. The position of the wafer chuck 104 in the X direction is monitored by an X-interferometer (not shown) for receiving light reflected by an X-mirror 107b mounted on one end of the Y-stage 103 in the X direction. An output from the X-interferometer is negatively fed back to an X-servo arithmetic unit (not shown). The X-servo arithmetic unit drives the X-driving unit to move the X-stage 102 in the X direction.
That is, the wafer chuck 104 is sequentially moved (step-moved) in the X and Y directions by necessary amounts while the positions of the wafer chuck 104 in the X and Y directions are monitored by light reflected by the X-mirror 107b and the Y-mirror 107a. With this operation, the wafer chuck 104 is moved to a position where a wafer is to be transferred, or each exposure region is positioned with respect to exposure light (not shown). In addition, the total gravitation of the Y-stage 103 is canceled out by the tensile force of the constant tension spring 106, whereby the load on each linear motor 105 can be reduced.
According to the above conventional technique, the constant tension spring for canceling out the gravitation of the Y-stage has a tensile force irregularity of ten-odd percent at maximum. The Y-stage has recently increased in weight with an increase in the diameter of a wafer. The total mass of the Y-stage is about several 10 to 100 kg. For this reason, a driving unit such as a linear motor which drives the Y-stage in the Y direction needs to have a thrust margin of several to ten-odd kg. In addition, since the maximum acceleration of the Y-stage is generally about 0.3 G, the maximum design value of the thrust for moving the Y-stage in the Y direction is 30 kg. The ratio of the above thrust margin to this design value is large. Consequently, the linear motor and the like must be considerably increased in size, and then the amount of heat generated by the linear motor may increase to cause thermal deformation of a substrate such as a wafer.
Furthermore, since the overall Y-stage is directly suspended by using the constant tension spring, the constant tension spring must be mounted at a position immediately above the Y-stage. If, therefore, dust is produced by friction between the constant tension spring and the rotating shaft around which the upper end of the spring is wound or friction occurs at the wound portion of the constant tension spring, the surface of a substrate such as a wafer may be contaminated.